1. Field of the Invention
The present invention relates generally to a shunt trip assembly for a circuit breaker and, more particularly, to a shunt trip assembly that is selectively lockable to prevent inappropriate shock-based tripping of a circuit breaker.
2. Description of the Related Art
Numerous types of circuit breakers are known and understood in the relevant art. Among the purposes for which circuit breakers are provided is to interrupt an electrical circuit on command or according to certain criteria. For instance, a given circuit breaker may be configured to interrupt a circuit during one or more specific overload conditions or under other conditions.
Circuit breakers typically include a set of movable electrical contacts that are placed into a compressive abutting relationship with a set of stationary contacts to complete an electrical circuit. If it is desired to interrupt the electrical circuit, the movable contacts are moved away from the stationary contacts by a tripping mechanism to break the electrical connection between the movable and stationary contacts and to interrupt the electrical circuit. Numerous types of tripping mechanisms exist and are often tailored to meet specific needs of particular applications.
For instance, a given circuit breaker may include a trip mechanism with a delayed trip feature provided by a bimetallic strip as well as an instantaneous trip implemented by a magnetic device. In multiple-pole circuit breakers, such tripping often involves rotation of a trip bar to unlatch the circuit breaker mechanism and rapidly separate the moveable contacts from the stationary contacts to interrupt the electrical circuit. In this regard, it is often desirable to additionally provide a trip button to manually rotate the trip bar to unlatch the circuit breaker mechanism during certain conditions. Such a trip button may be depressed manually or may be depressed by a tripping solenoid that is electrically operated by a remote button.
While such tripping solenoids operate reliably under many conditions, circuit breaker trip mechanisms employing such tripping solenoids are often subject to inadvertent tripping during shock loading of the circuit breaker. As is understood in the relevant art, a solenoid includes a plunger that is axially movable with respect to the solenoid housing. During shock loading of the circuit breaker, the plunger of the tripping solenoid can be induced to move with respect to the solenoid housing, which can result in the circuit breaker being tripped even though the tripping solenoid was in a deenergized condition. Such inappropriate tripping of a circuit breaker is to be particularly avoided in critical applications in which loss of power would create an unsafe or harmful situation. It is thus desired to provide a circuit breaker shunt trip apparatus that is resistant to shock loading yet is capable of engaging on command the trip button of a circuit breaker trip mechanism.
In accordance with the invention, a shock resistant breaker shunt trip apparatus is provided that includes a tripping solenoid and a locking solenoid that are in a substantially perpendicular operative arrangement with one another and are energized simultaneously to cause the plunger of the tripping solenoid to engage the trip button of a circuit breaker trip mechanism. The locking solenoid includes a locking plunger that is in mechanical interference with a longitudinally-oriented first abutment surface formed on the tripping plunger of the tripping solenoid. Such mechanical interference prevents the tripping plunger from engaging the trip button unless the locking solenoid is energized. When it is desired to trip the circuit breaker, the tripping solenoid and the locking solenoid are energized to cause the locking plunger of the locking solenoid to move out of mechanical interference with the first abutment surface of the tripping plunger and to translate the tripping plunger into contact with the trip button to trip the circuit breaker. A peripherally-disposed second abutment surface is provided on the tripping plunger to prevent the locking plunger from returning to its extended position prior to the tripping plunger returning to its retracted position, which might otherwise interfere with the function of the device.
An aspect of the invention is to provide a shunt trip assembly for a circuit breaker, the general nature of which can be stated as including a tripping solenoid having a tripping plunger, the tripping plunger being movable along a tripping path between a retracted position and an extended position, the tripping path having a tripping length, a locking solenoid having a locking plunger, the locking plunger being movable along a locking path between an extended position and a retracted position, the locking path having a locking length, the locking plunger in the extended position being disposed in mechanical interference with the tripping plunger, and the locking plunger in the retracted position being disposed out of mechanical interference with the tripping plunger.
Another aspect of the present invention is to provide a method of controlling the movement of a tripping plunger of a tripping solenoid in a shunt trip assembly of a circuit breaker, the tripping plunger being moveable along a tripping path between a retracted position and an extended position, the general nature of which can be stated as including the step of blocking movement of the tripping plunger from the retracted position to the extended position.
Another aspect of the invention includes providing, in combination, a circuit breaker and a shunt trip assembly, the general nature of which can be stated as including a circuit breaker and a shunt trip assembly operatively connected with the circuit breaker, the shunt trip assembly including a tripping solenoid having a tripping plunger, the tripping plunger being movable along a tripping path between a retracted position and an extended position, a locking solenoid having a locking plunger, the locking plunger being movable between an extended position and a retracted position, the locking plunger in the extended position being disposed in the tripping path, and the locking plunger in the retracted position being disposed out of the tripping path.
These and other aspects and advantages of the present invention will be more readily understood from the following description.